High power electrode materials

Abstract

An LFP electrode material is provided which has improved impedance, power during cold cranking, rate capacity retention, charge transfer resistance over the current LFP based cathode materials. The electrode material comprises crystalline primary particles and secondary particles, where the primary particle is formed from a plate-shaped single-phase spheniscidite precursor and a lithium source. The LFP includes an LFP phase behavior where the LFP phase behavior includes an extended solid-solution range.

The invention claimed is: 
     
       1. A method to form an ammonium iron phosphate for use to make an electrode active material, comprising:
 (a) introducing an iron (II) salt, a phosphate source, an ammonium source, and an oxidizing agent into an aqueous solution to form a mixture; 
 (b) filtering the mixture to recover a solid by-product; 
 (c) re-dispersing the solid by-product into an aqueous solution; 
 (d) heating the aqueous solution; 
 (e) filtering the solution to recover a solid; and 
 (f) drying the solid to obtain a high purity spheniscidite with a formula of NH 4 Fe 2 (PO 4 ) 2 OH.2H 2 O. 
 
     
     
       2. The method of  claim 1 , wherein the high purity spheniscidite is a single-phase. 
     
     
       3. The method of  claim 1 , wherein the high purity spheniscidite has a plate-shape morphology. 
     
     
       4. The method of  claim 1 , wherein the iron (II) salt is selected from iron (II) sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, or a mixture thereof. 
     
     
       5. The method of  claim 1 , wherein the phosphate source is selected from H 3 PO 4 , P 2 O 5 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NaH 2 PO 4 , Na 2 HPO 4 , Na 3 PO 4 , or mixtures thereof. 
     
     
       6. The method of  claim 1 , wherein the ammonium source is selected from NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NH 4 OH or mixtures thereof. 
     
     
       7. The method of  claim 1 , wherein the oxidizing agent is selected from H 2 O 2 , Na 2 O, NaClO 3 , or mixtures thereof. 
     
     
       8. The method of  claim 1 , further comprising rinsing the solid by-product and/or solid following filtering. 
     
     
       9. The method of  claim 1 , further comprising:
 (g) mixing the obtained high purity spheniscidite, a lithium source, a dopant, and a carbon source; 
 (h) adding a solvent to produce a slurry; 
 (i) milling the slurry; 
 (j) drying the milled slurry; and 
 (k) firing the dried milled slurry to obtain the lithium iron phosphate, wherein the lithium iron phosphate comprises a substantially olivine crystalline phase, a primary particle in the range of 20 nm to 80 nm, a secondary particle with d 50  in the range of 5 μm to 13 μm, and a surface area of 25 m 2 /g to 35 m 2 /g, and less than 5% by weight of carbon; and 
 wherein the lithium iron phosphate improves battery performance at low temperatures in comparison to current lithium iron phosphate materials. 
 
     
     
       10. The method of  claim 9 , wherein the slurry is milled to obtain primary particles of about 20 nm to about 80 nm. 
     
     
       11. The method of  claim 9 , wherein the solvent is water. 
     
     
       12. The method of  claim 9 , wherein the solvent is a compound comprising an alcohol functional group or water. 
     
     
       13. The method of  claim 9 , wherein the testing at low temperatures are at 0° C. or lower. 
     
     
       14. The method of  claim 9  having a carbon percentage of at least 2.1%. 
     
     
       15. The method of  claim 9  having a carbon percentage of about 2.1% to 2.5%. 
     
     
       16. A method to form crystalline spheniscidite material for use as an electrode active material, comprising:
 (a) introducing an iron (II) salt, a phosphate source, an ammonium source, and an oxidizing agent into an aqueous solution to form a mixture; 
 (b) filtering the mixture to recover a solid by-product; 
 (c) re-dispersing the solid by-product into an aqueous solution; 
 (d) heating the aqueous solution; 
 (e) filtering the solution to recover a solid; and 
 (f) drying the solid to obtain a high purity spheniscidite with a formula of NH 4 Fe 2 (PO 4 ) 2 OH.2H 2 O, wherein the crystalline spheniscidite material is an ammonium iron phosphate substantially free of impurities; and wherein the crystalline spheniscidite material has a plate-shape morphology. 
 
     
     
       17. The method of  claim 16 , wherein the high purity spheniscidite is a single-phase. 
     
     
       18. The method of  claim 16 , wherein the iron (II) salt is selected from iron (II) sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, or a mixture thereof. 
     
     
       19. The method of  claim 16 , wherein the phosphate source is selected from H 3 PO 4 , P 2 O 5 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NaH 2 PO 4 , Na 2 HPO 4 , Na 3 PO 4 , or mixtures thereof. 
     
     
       20. The method of  claim 16 , wherein the ammonium source is selected from NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NH 4 OH or mixtures thereof. 
     
     
       21. The method of  claim 16 , wherein the oxidizing agent is selected from H 2 O 2 , Na 2 O, NaClO 3 , or mixtures thereof. 
     
     
       22. The method of  claim 16 , further comprising rinsing the solid by-product and/or solid following filtering. 
     
     
       23. The method of  claim 16 , further comprising:
 (g) mixing the obtained high purity spheniscidite, a lithium source, a dopant, and a carbon source; 
 (h) adding a solvent to produce a slurry; 
 (i) milling the slurry; 
 (j) drying the milled slurry; and 
 (k) firing the dried milled slurry to obtain the lithium iron phosphate, wherein the lithium iron phosphate comprises a substantially olivine crystalline phase, a primary particle in the range of 20 nm to 80 nm, a secondary particle with d50 in the range of 5 μm to 13 μm, and a surface area of 25 m 2 /g to 35 m 2 /g, a carbon percentage of at least 2.1%; and 
 wherein the lithium iron phosphate improves battery performance at low temperatures in comparison to current lithium iron phosphate materials. 
 
     
     
       24. The method of  claim 23 , wherein the slurry is milled to obtain primary particles of about 20 nm to about 80 nm. 
     
     
       25. The method of  claim 23  wherein the solvent is water. 
     
     
       26. The method of  claim 23 , wherein the solvent is a compound comprising an alcohol functional group or water. 
     
     
       27. The method of  claim 14 , wherein the testing at low temperatures are at 0° C. or lower. 
     
     
       28. A method for synthesizing ammonium iron phosphate for use as an electrode active material in an electrochemical cell, comprising:
 introducing an iron (II) salt, a phosphate source, an ammonium source, and an oxidizing agent into an aqueous solution to form a mixture; 
 filtering the mixture to recover a solid by-product; 
 re-dispersing the solid by-product into an aqueous solution; 
 heating the aqueous solution at a temperature in a range of 85-95° C.; 
 filtering the solution to recover a solid; 
 drying the solid to obtain a high purity spheniscidite with a formula of NH 4 Fe 2 (PO 4 ) 2 OH.2H 2 O having a surface area in a range of 20-25 m 2 /g. 
 
     
     
       29. The method of  claim 28 , wherein the high purity spheniscidite has an XRD with no impurity peaks over 5%. 
     
     
       30. The method of  claim 28 , wherein the high purity spheniscidite comprises: ammonium in a first range of 4.6-5.0 wt. %, iron in a second range of 30-35 wt. %, and phosphorus in a third range of 15-20 wt. %. 
     
     
       31. The method of  claim 30 , wherein the high purity spheniscidite has a molar ratio of ammonium to phosphorus of 1.8:3.5, and a molar ratio of phosphorus to iron of 1:1.25. 
     
     
       32. The method of  claim 28 , wherein the aqueous solution of the re-dispersed solid by-product has a pH ranging from 1.8 to 3.1. 
     
     
       33. The method of  claim 28 , further comprising selecting the iron (II) salt from iron (II) sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, or a mixture thereof. 
     
     
       34. The method of  claim 28 , further comprising selecting the phosphate source from H 3 PO 4 , P 2 O 5 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NaH 2 PO 4 , Na 2 HPO 4 , Na 3 PO 4 , or mixtures thereof. 
     
     
       35. The method of  claim 28 , further comprising selecting the ammonium source from NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , NH 4 OH or mixtures thereof. 
     
     
       36. The method of  claim 28 , further comprising selecting the oxidizing agent from H 2 O 2 , Na 2 O, NaClO 3 , or mixtures thereof. 
     
     
       37. The method of  claim 28 , wherein the high purity spheniscidite has an XRD with no impurity peaks over 5%. 
     
     
       38. The method of  claim 28 , wherein the high purity spheniscidite has a surface area of 20-25 m 2 /g. 
     
     
       39. The method of  claim 28 , wherein the high purity spheniscidite has a plate-shape morphology. 
     
     
       40. The method of  claim 28 , further combing the high purity spheniscidite with a lithium source to form lithium iron phosphate having a particle size in a range of 20-80 nm.